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  <script>
    var arr = [2, 6, 1, 7, 4];
    var sum = 0;
    var arg;
    for (var i = 0; i < arr.length; i++) {
      sum += arr[i]; // 我们要加的是数组的元素 arr[] ，不是计数器 i
    }
    arg = sum / arr.length;
    // console.log(sum);
    // console.log(arg);
    console.log(sum, arg); // 想要输出多个变量，就用逗号分隔开即可
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